A busbar is typically a strip of conducting material for use in an electrical apparatus. A busbar may be electrically connected to a PCB to provide a return path for electrical current for electrical components on the PCB. Such a busbar is referred to herein as an earth busbar.
A busbar typically has a number of electrical connections to respective electrical contacts on a surface of a PCB. Most typically three electrical connections are made from the busbar to three respective electrical contacts on a PCB. Each connection is realized by a threaded screw, comprising a conductive material, which is inserted through a hole in the PCB and received into the busbar. The head of the screw contacts the respective electrical contact on the surface of the PCB. The first connection is a conventional earth connection, which will be used in most applications. The second connection is for connecting an electromagnetic compatibility (EMC) capacitor to earth. The third connection is for connecting a metal oxide varistor (MOV) to earth.
In some applications, it may be desirable not to have the second or third connection at least some of the time. For example, electrical noise in a circuit may be reduced by removing the EMC capacitor. An MOV provides protection from transient voltages, which may result from a lightning strike, for example. In some applications, for example on a ship, the power supply is isolated and so such protection is not required.
In applications where the second or third connection is not used, a sufficiently large gap between the second or third electrical contact on the PCB and the conducting material of the earth busbar must be maintained to ensure proper electrical clearance and to prevent current leakage from the PCB to the earth busbar. According to known methods, the gap is typically maintained by inserting an insulating spacer between the PCB and the earth busbar during installation.
The insulating spacer is typically formed of a thermoplastic material. The spacer is therefore subject to creep over time, which can cause the connector between the PCB and the busbar to come loose, resulting in a poor electrical connection. Furthermore, the spacer adds complexity to the installation process, and is sometimes omitted from the installation entirely because of human error. When the spacer is omitted, leakage currents can flow between the PCB and the busbar even when no connecting screw has been installed, producing unpredictable and undesirable consequences.
An invention is set out in the claims.